Fwd: [HPAC SC] Interesting new reason leading to retreat of clouds and Earth's albedo

[Ron Baiman]

Wow! Good catch Mike. I'm taking the liberty of sending this out to the list as I think it's important. 

Best,

Ron

---------- Forwarded message ---------
From: Michael MacCracken <mmac...@gmail.com>
Date: Fri, Oct 3, 2025 at 9:21 AM
Subject: [HPAC SC] Interesting new reason leading to retreat of clouds and Earth's albed! 

A note from Heatmap--second paragraph quite interesting:

4. Antarctic sea ice shrinks to third-lowest winter peak

Sea ice in Antarctica reached its third-smallest winter peak extent since satellite records began 47 years ago, according to a new analysis by Carbon Brief. Provisional data from the U.S. National Snow and Ice Data Center showed Antarctic sea ice reaching a winter maximum of just under 6.9 million square miles as of September 17. That’s nearly 350,000 square miles below the average between 1981 and 2010, the historical baseline against which recent changes in sea ice extent are compared. The “lengthening trend of lower Antarctic sea ice poses real concerns regarding stability and melting of the ice sheet,” one expert told the publication.  The finding comes as a “groundbreaking” study the European Geosciences Union published Thursday in the journal Earth System Dynamics found that Antarctic sea ice has emerged as a key predictor of accelerated ocean warming. Using Earth system models and satellite images from 1980 to 2020, the researchers found higher sea ice extent enhances cloud cover, which has a cooling effect overall by reducing incoming solar radiation. As a result, ongoing sea ice loss is linked to larger reductions in clouds, stronger surface warming, and even more ocean heat uptake, accelerating the cycle.

Best, Mike

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[Robin Collins]

It’s a bit of a circular argument though:

“higher sea ice extent enhances cloud cover, which has a cooling effect overall by reducing incoming solar radiation. As a result, ongoing sea ice loss is linked to larger reductions in clouds, stronger surface warming, and even more ocean heat uptake, accelerating the cycle.”

So why does reduced sea ice cause increased clouds?

Robin

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[Jan Umsonst]

Hi all, 

you can see it nicely in 2023 the year of maximum loss - also it correlates nicely with the projected regions - here where clouds declined in 2023:

Source: "recent global temperature surge intensified by record low planetary albedo" https://www.science.org/doi/10.1126/science.adq7280 

Next a graph of where the clouds decline due to sea ice losses and Southern Ocean warming - its (f):

Source: "

Increased future ocean heat uptake constrained by Antarctic sea ice extent"; https://esd.copernicus.org/articles/16/1453/2025/

Here a study from 2023 on the Southern Ocean SST-cloud feedback which shifted into its warming mode by the recent warming trend of the Southern Ocean: 

Here we demonstrate a mechanism whereby the Southern Ocean controls the global climate feedback. [...] This global impact is mediated by a teleconnection to the Southeast Pacific, where remote sea surface temperature anomalies cause a strong stratocumulus cloud feedback. We propose that this Southern Ocean-driven pattern effect is underestimated in most climate models, owing to an overly weak stratocumulus cloud feedback. Addressing this bias may shift climate sensitivities to higher values than currently simulated as the Southern Ocean undergoes accelerated warming in future projections.

"Recent global climate feedback controlled by Southern Ocean cooling"; https://www.nature.com/articles/s41561-023-01256-6

And its the recent years the Southern Ocean is warming now and its connected with sea ice loss: 

Our results reveal that the primary cause of this decline is ocean warming in the subpolar and mid‐latitude regions near the ice edge, which inhibits sea‐ice advance. Wind also contributes to sea‐ice variability, particularly in summer.

"Causes of the Abrupt and Sustained 2016–2023 Antarctic Sea-Ice Decline: A Sea Ice–Ocean Model Perspective"; https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL115256

But it comes even better:

Cloud supporting aerosol load is decreasing in the Northern Hemisphere, while it increased in the Southern Hemisphere - here a recent preprint on the matter: 

 While previous studies, based on single-forcing (aerosol-only) experiments, linked reductions in anthropogenic aerosols to this positive SW trend, we find that both aerosol-radiation interactions and aerosol-cloud interactions have had a negligible impact on recent increases in the EEI. We estimate recent trends in effective radiative forcing due to aerosols using observations and reanalysis data. While aerosol concentrations have declined in the Northern Hemisphere (NH), wildfires and volcanic activity in the Southern Hemisphere (SH) have resulted in larger aerosol loading. This contrast effectively cancels out the total aerosol forcing, resulting in a negligible global impact on the EEI trend.

"Negligible Contribution from Aerosols to Recent Trends in Earth’s Energy Imbalance"; https://www.researchsquare.com/article/rs-5679586/v1

And here a recent published study with a similar finding - Earths albedo symmetry is breaking - but while aerosols decrease over the NH, they increased in the SH with a negligible contribution from cloud radiative effects to the faster darkening of the NH.

This means that it could be that the SH cloud cover reaction much stronger to warmer surface temperatures than in the NH, because of much larger ocean areas:

The reason for the weak hemispheric contrast in the ASR trend contribution from cloud changes is less clear. [...] The SH is the cloudier hemisphere, so perhaps it responds more in an absolute sense to increases in surface temperature than the NH, whose greater landmass may also buffer any hemispheric albedo decrease from reduced cloud cover.

"Emerging hemispheric asymmetry of Earth’s radiation"; https://www.pnas.org/doi/full/10.1073/pnas.2511595122

Here the shit show in graphs - northern Hemisphere a decrease (warming via cloud effect) while in the SH a increase (cooling via cloud effect):

And here the cloud feedback in both Hemispheres:

Source: "Emerging hemispheric asymmetry of Earth’s radiation"; https://www.pnas.org/doi/full/10.1073/pnas.2511595122

And here comes the catch - warm water is coming up around Antarctica again since several years - signal reversed - sea ice feedback, and a cloud feedback, feeding back on ocean heat uptake and ocean surface warming feeding back on sea ice...:

Source: "Pacific sub-decadal sea surface temperature variations contributed to recent Antarctic Sea ice decline trend"; https://www.nature.com/articles/s41467-025-58788-1

This warm water signal seems to be driven by a sudden reversal of surface saltiness - the surface waters got saltier, denser, vertical mixing intensified and starts now to mix warm subsurface waters into the upper mixed layer - here this study:

For decades, the surface of the polar Southern Ocean (south of 50°S) has been freshening—an expected response to a warming climate. This freshening enhanced upper-ocean stratification, reducing the upward transport of subsurface heat and possibly contributing to sea ice expansion. It also limited the formation of open-ocean polynyas. Using satellite observations, we reveal a marked increase in surface salinity across the circumpolar Southern Ocean since 2015. This shift has weakened upper-ocean stratification, coinciding with a dramatic decline in Antarctic sea ice coverage.         

"Rising surface salinity and declining sea ice: A new Southern Ocean state revealed by satellites"; https://www.pnas.org/doi/10.1073/pnas.2500440122

Here the graph (compare this with the graph in the above study with surface waters warming - perfect match - the problem is that the warm water mixed into the surface layer is also saltier thereby its self-sustaining this signal:

Its a nice example of the perfect storm that is now building up inside the Earth system and we can only hope that we can stall it for some time with SRM...

All the best

Jan

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[Robin Collins]

I am not doubting the correlation.  I’m asking for the causation — the explanation.

Robin 

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[Robin Collins]

Apologies, I misread the original. More ice means more clouds (not fewer). 

But can I still have a cause for this nonetheless? 😀

Robin 

[Jan Umsonst]

Hi all, accordingly to literature its the opposite - less sea ice, warmer Southern Ocean leading to less clouds over the Southern Hemisphere. 

Also via the SST pattern effect - this is another study on the sea ice-southern Hemisphere SST-cloud feedback complex. The pattern effect could be stronger than previously estimated (a more even zonal (east/west) SST distribution reduces tropospheric stability which then supports convection thereby reducing low cloud  cover over the oceans which have a stronger cooling effect than convective clouds and their upper cloud decks):

Southeast Pacific and Southeast Atlantic SST warming leads to a greater tropical/subtropical cloud feedback - sea ice losses also could also contribute to it:

Tropical marine low cloud feedback is key to the uncertainty in climate sensitivity, and it depends on the warming pattern of sea surface temperatures (SSTs). Here, we empirically constrain this feedback in two major low cloud regions, the tropical Pacific and Atlantic, using interannual variability. Low cloud sensitivities to local SST and to remote SST, represented by lower-troposphere temperature, are poorly captured in many models of the latest global climate model ensemble, especially in the less-studied tropical Atlantic. The Atlantic favors large positive cloud feedback that appears difficult to reconcile with the Pacific—we apply a Pareto optimization approach to elucidate trade-offs between the conflicting observational constraints. Examining ~200,000 possible combinations of model subensembles, this multi-objective observational constraint narrows the cloud feedback uncertainty among climate models, nearly eliminates the possibility of a negative tropical shortwave cloud feedback in CO₂-induced warming, and suggests a 71% increase in the tropical shortwave cloud feedback.

"Multi-objective observational constraint of tropical Atlantic and Pacific low-cloud variability narrows uncertainty in cloud feedback"; https://www.nature.com/articles/s41467-024-53985-w

Best to all

Jan

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[Jan Umsonst]

Hi all,

one cause seems to be the pattern effect - warmer SSTs in the Southeast Pacific and Southeast Atlantic. Further, warmer sea surface temperatures across the mid-latitudes are related to less cloud cover - dries out the upper boundary layer where clouds form.

And it could be that extratropical marine heatwaves during the warmer months support high pressure systems which also reduce cloud cover.

Here two studies on the extratropical cloud effect by warmer SSTs - the pattern effect I posted one of the relevant studies - as it comes in addition:

The first is how mid-latitude SSTs reduce cloud cover:

 "Observational and Model Evidence for Positive Low-Level Cloud Feedback"; Amy C. Clement, Robert Burgman, and Joel R. Norris; Science, vol. 325, 2009; DOI: 10.1126/science.1171255; online: https://www.science.org/doi/10.1126/science.1171255 (08.14.2025)

This could be one mechanism: the upward emitted longwave radiation dries out the boundary layer where clouds form:

"Positive Low Cloud Feedback Primarily Caused by Increasing Longwave Radiation From the Sea Surface in Two Versions of a Climate Model"; Tomoo Ogura, Mark J. Webb, Adrian P. Lock; Geophysical Rrsearch Letters, vol. 50, 2023; DOI: 10.1029/2023GL104786; online: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL104786 (08.15.2025)

Then it could be that higher SSTs in the extratropics cause a low convective environment during summer which then supports high pressure systems/or that that a higher air column over extratropical marine heatwaves redirects the jets poleward thereby supporting blocking patterns which then support the MHWs to persist - so via the alteration of large scale circulation a cloud feedback over the abnormal warm oceans (not clear - is just coming into focus of science as these large summer marine heatwaves are new and the effects on the atmosphere are far from clear). Further, sea ice losses could support a wave 3 pattern over the Southern Hemisphere, which supports blocking and high pressure triggering the circumpolar summer marine heatwaves around Antarctica which then also lead to reduced cloud cover via direct high pressure and secondary via SST-cloud feedback over MHWs.

So its basically via two avenues: local effects reducing cloud cover and large scale atmospheric alterations of flow patterns or atmospheric stability over large ocean areas...

All the best

Jan

[Jan Umsonst]

Hi all, this discussed cause of the extratropical (tropical) cloud feedback I forgot:

The storm tracks (should be during the colder months) shift poleward thereby the mid latitude clouds bands are contracting, as the tropical rain belt does - the intertropical convergence zone.

In the Souhtern Hemisphere the Southern Annular Mode (SAM - circumpolar circulation around Antarctica) is shifting to its positive mode, which causes it to move closer to Antarctica (contract) and intensify:  

The results show that the circulation component of the cloud radiative changes, which manifests itself as a contraction of the midlatitude storm zones and the tropical rainy zone, is the dominant term in the solar reflection trend causing decreased sunlight reflection of 0.37 W/m2 per decade. The discovery of this component provides a crucial missing piece in the puzzle of the 21st century increase of the Earth’s Energy Imbalance and points to the large effect that even small atmospheric circulation changes have on the Earth’s warming climate.


Source: "Contraction of the world’s storm-cloud zones the primary contributor to the 21st century increase in the Earth’s sunlight absorption"; https://www.researchsquare.com/article/rs-5050391/v1

 

The graph from this NOAA article: https://www.earthobservatory.nasa.gov/images/154443/earths-clouds-on-the-move 

All the best

Jan

On 10/3/25 22:27, Robin Collins wrote:

[PR CARTER]

Another driver of global warming acceleration-which will only increase 

It's increasingly clear that accelerating global warming requires cooling, but governments will not allow it

The main thing is to get the already collapse across

Best regards 

Peter C

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From: "Jan Umsonst" <j.o.u...@gmail.com>
To: "Robin Collins" <robin.w...@gmail.com>
Cc: healthy-planet-...@googlegroups.com
Sent: Friday, October 3, 2025 3:15:43 PM
Subject: Re: [HPAC] Fwd: [HPAC SC] Interesting new reason leading to retreat of clouds and Earth's albedo

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[John Nissen]

Hi Peter,

Global warming is accelerating, which demands effective cooling.  Yes!

"But governments won't allow it".  Sadly you are right.  Certainly one or more governments are going to have to give permission for cooling intervention, if not actually funding it.  With SAI it might only need to be one government for cooling the Arctic, since the SO2 spreads northward from mid latitudes according to the Brewer-Dobson circulation.  The aerosol spreads quickly around the planet in an easterly direction, while spreading slowly towards the pole before sinking into the troposphere.  Everyone in the Northern Hemisphere would obtain the cooling benefit.  (I haven't been following the arguments about effects on monsoons, but a restoration of balance between hemispheres is likely to be beneficial to everyone.  The northern hemisphere has been warming faster than the southern, which has affected the ITCZ.  There also seem to have been some adverse effects on cloud cover which is the subject topic of this thread.)

There is going to have to be great pressure put on any government to persuade it to prepare for and deploy SAI.  At present the few people strongly advocating for cooling intervention are a disparate lot.  And those advocating for emergency SAI to refreeze the Arctic are even fewer.  But the arguments for emergency SAI are overwhelming if you take into account the mounting suffering in many poorer countries, especially in the Global South.  SAI advocacy would be good value for philanthropists who are seeking the most effective use of their money (the money being spent on advocacy rather than actual deployment).  And SAI would help to prevent catastrophic sea level rise in the future.  It could also lower global temperatures and reverse climate change.  So there are potentially huge benefits for everyone.

Apart from governments, the only group with enough money to actually fund SAI deployment is the fossil fuel industry.  They also have an engineering mindset and relevant engineering expertise.  So I welcome their contribution to the debate.  

Cheers, John

 

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